Nonlinear stability analysis of piecewise actuated piezoelectric microstructures

The main objective of this research is to provide a general nonlinear model of adjustable piezoelectric microwires with the ability to tune the stability conditions. In order to increase the controllability and improve system characteristics, only a part of the substrate is electrostatically actuated and the piezoelectric voltage is also applied. The governing equation of equilibrium (EOE) is derived from the principle of minimum total potential energy. The influences of the surface layer, size dependency, piezoelectricity, and dispersion forces are also included simultaneously. To solve the nonlinear differential equation, a numerical method is implemented and the obtained results are validated with available experimental and numerical results. Afterward, a set of parametric studies is carried out to examine the coupled effects of piezo-voltage, length/position of non-actuated pieces, nonlinear curvature, and molecular forces on the microresonators. It is found that the beam deflection and the pull-in voltage have sensitive-dependence on the system behavior. Furthermore, the beam deflection can increase or decrease with consideration of different positions of non-actuated pieces. This research is expected to fill a gap in the state of the art of the piezoelectric microstructures and present relevant results that are instrumental in the investigation of advanced actuated microdevices

Modelling of Self-Sensing Hybrid Composites for Detection of Barely Visible Impact Damage

Barely visible impact damage (BVID) may decrease by up to 60% compressive strength of laminates compared with an undamaged laminate. Hence, BVID detection and its extent is an essential yet expensive task in the inspection of laminates. In this study, a finite element (FE) model is developed to simulate a novel hybrid composite with BVID self-sensing ability. The hybrid composite is made of a quasi-isotropic T800 carbon/MTM49-3 epoxy laminate with a surface integrated sensing layer consisting of single plies of unidirectional ultra-high modulus carbon (YS-90)/epoxy and S-glass/epoxy material. The sensing layer experiences visually detectable damage earlier or at the same time as BVID. The induced damage in the sensor is ultra-high modulus carbon fracture followed by incremental crack growth at the carbon/glass interface and splits in the glass layer along the fibres. Modified cohesive elements with a user-defined subroutine are used in LS-Dyna software to simulate the damage sequence. The developed FE model is validated experimentally, and the results show direct relationships between visible damage in the sensing layer and internal hidden damage observed by C scan and simulated by the FE model. This offers self-sensing composites with cost effective and more durable BVID detection capacity than the current technologies